1. Field of the Invention
The present invention relates to a mixed topology data switching system that combines a radial interconnect with a ring interconnect. More particularly, the radial interconnect permits devices to store and retrieve data using a switch, while the ring interconnect permits devices along the ring interconnect to provide notification that data has been stored for retrieval, as well as provide feedback regarding the ability or inability to retrieve such data.
2. Description of the Related Art
Although parallel busses may be advantageously used to convey data among devices, there are limits to the speed with which data may be transmitted. In order to increase the speed with which data is conveyed, previous approaches have typically centered around the use of wide parallel busses. However, as aggregate system bandwidths increase, these wide, long busses become problematic due to high pin counts and capacitance loading. Control pins as well as data pins must typically be provided, further increasing the width of the bus. It would therefore be desirable if the conveyance of data could be optimized while reducing the number of pins required.
Another commonly used data transport system is the ring. For instance, in a token ring, a single token circulates around the ring. In order to send a unit of data, a device must remove this token from the ring and replace it with the data to be transmitted. The permission to transmit rotates around the ring in a round-robin fashion. It is important to note that the ring typically provides only one token. As a result, only one device can transmit data at a given instant.
A drawback common to both parallel busses and rings is that each must be able to accommodate the aggregate of the entire system""s data transfer volume even though only a small subset of the attached devices on these interconnect systems may actually need to be involved in the data transaction. In other words, the data cannot be sent directly to only those interfaces to which the data is addressed. Rather it is broadcast to all nodes on the interconnect system. Accordingly, it would be desirable if a system capable of limiting the distribution of unnecessary data to interfaces on an interconnect scheme could be implemented.
In controlling the flow of network traffic through a switching system, it is often desirable to provide feedback to the source of the data. For instance, although a transmitting device, hereinafter referred to as a xe2x80x9csource device,xe2x80x9d may transmit or forward data to a receiving device, hereinafter referred to as a xe2x80x9cdestination device,xe2x80x9d the destination device may be incapable of handling the data. In these circumstances, the source device is often unaware that the data was not accepted by the destination device, complicating switch management. Common solutions to the problem of switch traffic management have included ensuring that all intended destination devices are xe2x80x9cready to receivexe2x80x9d prior to transmitting data on a ring or bus interconnect, or insisting that each intended destination device send an explicit acknowledgement back to the source device. Both of these approaches result in reduced efficiency of the interconnect scheme. By way of example, in a ring network, such acknowledgment is typically provided in the data frame being transmitted. As another example, in other interconnect schemes, each such device may send a separate acknowledgment, therefore adding to the traffic on the network. Accordingly, it would be desirable if a traffic management scheme were established which could provide such feedback to the source of the data while minimizing traffic management overhead.
According to one embodiment, the present invention combines the use of two data transport methods: a point-to-point radial interconnect and a ring interconnect. The radial interconnect connects interface devices to each other through the services of a central switch device to permit the transport of data. Typically, a single interface has a single dedicated radial interconnect to the central switch. These interface devices are further connected to one another via a ring interconnect to convey retrieval notifications regarding forwarding of the data (by source devices) and receipt of the data (by destination devices).
Each radial interconnect provides a narrow, high baud-rate connection to convey the actual data from and to the associated interface without being burdened by the unrelated traffic for the remaining interfaces in the system. This is accomplished through the use of a central switch device, which stores and retrieves data for the various interfaces in the system. As will be apparent from the following description, this architecture provides numerous advantages over a wide parallel bus or ring.
The ring interconnect may be used to convey a xe2x80x9cretrieval notificationxe2x80x9d (i.e., retrieval message) that may be observed by all potential retrieving interfaces. The retrieval notification notifies specific devices (xe2x80x9cdestination devicesxe2x80x9d) or interfaces that one or more frames addressed to them are available from the switch device. Moreover, the ring interconnect permits each destination device to provide feedback to the source device letting the source know whether the destination has accepted the notification provided by the source device and therefore whether the destination can retrieve the data intended for it. The feedback is particularly useful in buffer management applications. In this manner, an efficient and flexible data transport and retrieval notification system that includes a feedback path to the source of the data is provided.
The source interface device and destination interface device may be implemented separately or in combination. According to one aspect of the invention, a method of enabling communication between the source interface device and one or more destination interface devices includes sending data from the source device to the switch for storage. A frame notify message addressed to the one or more destination devices and indicating that the data has been stored by the switch for retrieval is then sent on the ring interconnect.
Once the frame notify message is placed on the ring interconnect, each destination device specified in the frame notify message may obtain information from the frame notify message so that it may retrieve the data stored by the switch. According to another aspect of the invention, one of the destination interface devices obtains the frame notify message from the source device via the ring interconnect. A frame retrieval message identifying the data is then sent from the device to the switch in response to the frame notify message.
According to yet another aspect of the invention, the destination interface device modifies the frame notify message to indicate whether the destination device was capable of accepting the frame notify message. The modified frame notify message is then sent on the ring interconnect for retrieval by another destination device or the source device.